One good reason

In case you don’t feel like reading about it, it’s a free (for personal use) end-to-end encrypted VOIP client. There may be other methods out there, including personal Asterix PBXs, but this seems to work with the least fuss. Google Voice may or may not work with it I believe, as native SMS’ing must be working by default on the phone. To test I used my native phone number instead of my GV number, it worked fine over data.

UPDATE: As of late November 2011 it appears RedPhone has been pulled from the Android Market and the app itself can no longer connect to Whisper Systems’ servers. The application was in Beta, so this could mean there is a full release coming out or perhaps something required that it be pulled from the Android Market. So for right now, I’m unaware of any other end-to-end encrypted VOIP applications for Android.